|Carbon Steer Tube Flex||johnc|
Jan 10, 2002 10:26 AM
|I just put a Look carbon fork on my bike with the max allowed 2 cm of spacers in order to obtain the appropriate bar height. It flexes quite a bit when I'm out of the saddle pedaling and rocking the bike. Other than removing some or all of the spacers and lowering the stem, is there anything I can do to decrease the flex?|
Jan 10, 2002 11:11 AM
|Sorry I don't have an answer but I'm considering a Look fork and i was afraid of this very issue. Is it an HSC 3 and did it have a 1 inch steerer?|
Jan 10, 2002 12:35 PM
|Yep and Yep.|
|re: Carbon Steer Tube Flex||sherpa23|
Jan 10, 2002 11:42 AM
|I am assuming that you have a 1" steerer because there would be little flex in a 1.125". If I am wrong, please correct me. If you have a longer head tube (15-16cm or so) and a 1" carbon steerer, there is going to be flex no matter what - spacers or no spacers. If you have a shorter head tube, then you can try a different fork and there may be a small difference but you would have to have a 12 cm or shorter head tube and no spacers for it to be better. 1" carbon steerers on bigger bikes are bad ideas, imo, and not the best things on smaller bikes. I don't know of any other solutions. If someone mentions sticking a piece of wood in there (I know, but I have seen people post this as actual advice) tell them to stick it up their you-know-whats because the fork is going to snap off at the crown sooner rather than later and you will be really hurt or dead.|
|speaking about sticking it up the||cyclopathic|
Jan 10, 2002 7:51 PM
|I wonder if Look makes reinforcement plugs of if you can get aftermarket one. Certainly wood would work.
Crown separation? hmm Manitou had a recall last year problem with crown/steer separation guess what they did? put a Al plug
|speaking about sticking it up the||sherpa23|
Jan 11, 2002 7:49 AM
|Here's why sticking a reinforcement in the steerer will kill you: The steerer tube, from bottom to top, absorbs all the flex and bending and disperses the force throughout the full length of the tube. Due to the dispersion, none of the force in any one area is enough to break the tube. The moment that you put something in the steerer, like any kind of reinforcement, like a wooden dowel, you will concentrate all of that force at the crown. So where you previously had (for example) 12 n/m of pressure, you would now have as much as 10 times that. On a carbon steerer that means SNAP!!|
|have you ever seen one?||cyclopathic|
Jan 11, 2002 9:58 AM
|they usually fail in places were forces applied at crown/steer connection or alone sharp edges/headset races.
Plug should go deeper then headset races on both sides and fit tight, gluing highly recommended.
Given options he has (ditch the fork or leave with flex) I would epoxy in a plug. If you really wanna get fancy you can use fiberglass or kevlar cloth and epoxy and form the plug in place, 2-4 layers would be enough. Out of epoxies I'd use J-B Weld, ~4$ @ Walmart it has the highest holding power.
|re: Carbon Steer Tube Flex||gtx|
Jan 10, 2002 12:51 PM
|I'd try a new stem with more rise--aim for no spacers. You will need to dust off the high school math to figure out what will be appropriate and then shop around for a stem with the right rise/length combo.|
Jan 10, 2002 1:22 PM
|I've been warning people about this for some time. The 1" LOOK carbon steerer tubes ARE quite flexy. |
You're screwed unless you can stomach an upturned stem.
|doesn't always look so bad...||gtx|
Jan 10, 2002 1:31 PM
Not sure if a steel stem is recommended with a carbon steerer (though Steelman uses them with the Reynolds forks). And of course I like the looks of a standard (-17 rise) quil stem better. And I like steel forks. :)
|doesn't always look so bad...||CT1|
Jan 10, 2002 1:43 PM
|IMHO, that type of stem rise is OK on a cross bike (need the extra clearance) but it looks WAY wrong on a "road" bike. You often see this type of setup on bikes that are the wrong size. |
I guess this is "to each his own" sort of thing.
Jan 10, 2002 1:45 PM
|doesn't always look so bad...||RayBan|
Jan 11, 2002 6:17 AM
|I've noticed a decent amount of pros have more rise on their stems than I assumed there would be in the pro peleton....|
|re: Carbon Steer Tube Flex||grzy|
Jan 10, 2002 2:16 PM
|>Other than removing some or all of the spacers and lowering the stem, is there anything I can do to decrease the flex? |
Buy a different fork with 1-1/8" diameter? I'm willing to bet that much of the flex that you notice comes from the stem and thin walled aluminum handle bars. Recognize that the kind of spacers you use and the preload that you place via the compression bolt will have a lot to do with the "stiffness" of the entire assembly. CF is great in tension, but not so good in compression - are you using aluminum spacers for your 2 cm of height? I run almost 3 cm of aluminum spacers, a Reynold Ouzo Pro, Ritchey WCS stem, and Deda 215 bars and have very little flex. The load required to actually make the CF steerer flex is quite significant when one does the analysis - most bars are noodles in comparison. There is also a lot of variation in stems. My buddy runs a custom ti stem from Seven and the thing is like limp dish rag - you can see it move. FWIW - he still waxes me on the descents.
|grzy... tell me more about the compresion issue with CF...||Geof|
Jan 10, 2002 6:52 PM
|I run carbon spacers, just cause they look kinda kewl. What sort of issues am I looking at doing this? I have no problem with the alum ones... weight is not the issue, how much difference is there between the two? Is this applicable with mtb's as well? IE: carbon spacers on an aluminum steerer? (I've noticed it's more difficult to keep my CK headset correctly tensioned and figured oh well, is it the spacers?) I have the Look HSC3 1-1/8 and really notice my bars flex much more than anything (I run 46cm bars) more torque to get the things going. Anyway... Wha's up???
|grzy... tell me more about the compresion issue with CF...||grzy|
Jan 11, 2002 1:35 PM
|CF isn't good in compression. You're squishing and epoxy matrix which is fairly soft and can be made really soft with just a little heat. The thing that makes CF so kewl is that the indiviual fibers of carbon are so strong in *tension* - in compression aluminum is much better. As a simple test I'd try using just aluminum spacers and see if you notice the difference. be advised that if your stem/tension bolt setup doesn't hold a setting then everything above is moot.|
|re: GRZY-your thoughts...||johnc|
Jan 11, 2002 7:54 AM
|GRZY-I'm using 2 aluminum spacers, a Ritchey Pro Stem and bars. I'm not sure where the flexing is coming from, but the main problem is that my front wheel rubs against the brake pads anytime I stand on the pedals and rock the bike (I should have been more specific in my original post). This did not happen at all with my steel fork. Any further thoughts on this?|
|re: GRZY-your thoughts...||grzy|
Jan 11, 2002 1:46 PM
|Well, any flexing the stem, bars or steerer would have zero effect on your front wheel rubing on the pads. This is going to be strictly a function of the stiffness of the fork *blades* (you didn't say what you were running), the skewers and your wheel. Off hand I'd first look at the skewer that you use if it's not tight or if it's really wimpy (i.e. titainium) then the wheel will deflect under load. It is very common to get some gucci aftermarket skewers only to find that they don't have the stiffness to properly secure your wheel. Try something out of steel from Shimano or Mavic - others may work as well - I've had great expereince with these. Found that the ultra light gucci Control Tech Ti skewers that use an Allen wrench and weigh almost nothing are total crap - they even warn you not to tighten them too much or you may break them. Not exactly confidence inspiring. Even a low-end steel MTB skewer should hold the wheel fairly securely. Next thing to look at is the spoke tension and build of the front wheel - is it a noodle or something fairly bomber - is the wheel even true and round? Finally what kind of fork are you running - the lightest noodle around from Look or something more robust like a Kestrel or a Reynolds? |
With a little bit of thought and some careful part swaps and some test rides you should be able to isloate the culprit - it's usually just one item - the weakest link of the chain, as it were.
|re: GRZY-your thoughts...||jonc|
Jan 11, 2002 2:15 PM
|Thanks for your input. It's the Look HSC 3 with a Rolf Vector Comp wheel. The wheel is perfectly straight and round. Again, I did not have this problem with my steel fork that was just replaced. Any further ideas?|
|sure it's the steering tube???||C-40|
Jan 10, 2002 3:34 PM
|There is no way to easily distinguish what portion of bar flexure is due to the steering tube, the stem or the bars individually. They work together as a system. The bars or stem could be equally to blame.
You might want to revise your climbing technique. Applying excessive pressure to the bars is generally a waste of energy. While many climbers rock the bike on difficult climbs, the pressure required to do this is minimal and shouldn't create a great amount of flex.
|sure it's the steering tube???||tr|
Jan 10, 2002 4:23 PM
|I agree with C-40, i rock my bike with minimal force on the bar/stem/steering tube and i don't feel like my Reynold's carbon steerer (1 inch) is flexy. But, if that is not an option for you, then i guess you will have to fix it some other way.|
|I've never undestood...||Geof|
Jan 10, 2002 6:55 PM
|How people "flex" the front ends so much on a bike. I agree, it just may be more of a riding technique problem. Try not to "leverage" yourself on your climbs. Either gear down, or use a lighter touch to "rock" your bike.|
|re: Carbon Steer Tube Flex||RayBan|
Jan 11, 2002 6:13 AM
|One thing you can try that WILL work, is get a stem that has a higher rise and eliminate am many of the spacers between the stem and frame that you can. Ive ridden with an ITM stem that had a sleeve inside that would alter the rise on the stem with a twist of the sleeve before installing.|
|re: Carbon Steer Tube Flex||sticky|
Jan 11, 2002 7:15 AM
|I've just fitted an HSC3 fork (1" steerer). I don't seem to have more flex than before with a steel steerer. I had some flex in bars, and still do (Prima 199 flex a bit!)
I'm not sure any other 1" carbon steerer forks are any better.